${\sqrt{81} = \text{?}}$
Explanation: $\sqrt{81}$ is the number that, when multiplied by itself, equals $81$ If you can't think of that number, you can break down $81$ into its prime factorization and look for equal groups of numbers. So the prime factorization of $81$ is $3\times 3\times 3\times 3$ We're looking for $\sqrt{81}$ , so we want to split the prime factors into two identical groups. Notice that we can rearrange the factors like so: $81 = 3 \times 3 \times 3 \times 3 = \left(3\times 3\right) \times \left(3 \times 3\right)$ So $\left(3\times 3\right)^2 = 9^2 = 81$ So $\sqrt{81}$ is $9$.